Vlastimil Hart

Dogs are sensitive to small variations of the Earth’s magnetic field

IntroductionSeveral mammalian species spontaneously align their body axis with respect to the Earth’s magnetic field (MF) lines in diverse behavioral contexts. Magnetic alignment is a suitable paradigm to scan for the occurrence of magnetosensitivity across animal taxa with the heuristic potential to contribute to the understanding of the mechanism of magnetoreception and identify further functions of magnetosensation apart from navigation. With this in mind we searched for signs of magnetic alignment in dogs. We measured the direction of the body axis in 70 dogs of 37 breeds during defecation (1,893 observations) and urination (5,582 observations) over a two-year period. After complete sampling, we sorted the data according to the geomagnetic conditions prevailing during the respective sampling periods. Relative declination and intensity changes of the MF during the respective dog walks were calculated from daily magnetograms. Directional preferences of dogs under different MF conditions were analyzed and tested by means of circular statistics.ResultsDogs preferred to excrete with the body being aligned along the North–South axis under calm MF conditions. This directional behavior was abolished under unstable MF. The best predictor of the behavioral switch was the rate of change in declination, i.e., polar orientation of the MF.ConclusionsIt is for the first time that (a) magnetic sensitivity was proved in dogs, (b) a measurable, predictable behavioral reaction upon natural MF fluctuations could be unambiguously proven in a mammal, and (c) high sensitivity to small changes in polarity, rather than in intensity, of MF was identified as biologically meaningful. Our findings open new horizons in magnetoreception research. Since the MF is calm in only about 20% of the daylight period, our findings might provide an explanation why many magnetoreception experiments were hardly replicable and why directional values of records in diverse observations are frequently compromised by scatter.

Magnetic Alignment in Carps: Evidence from the Czech Christmas Fish Market

While magnetoreception in birds has been studied intensively, the literature on magnetoreception in bony fish, and particularly in non-migratory fish, is quite scarce. We examined alignment of common carps (Cyprinus carpio) at traditional Christmas sale in the Czech Republic. The sample comprised measurements of the directional bearings in 14,537 individual fish, distributed among 80 large circular plastic tubs, at 25 localities in the Czech Republic, during 817 sampling sessions, on seven subsequent days in December 2011. We found that carps displayed a statistically highly significant spontaneous preference to align their bodies along the North-South axis. In the absence of any other common orientation cues which could explain this directional preference, we attribute the alignment of the fish to the geomagnetic field lines. It is apparent that the display of magnetic alignment is a simple experimental paradigm of great heuristic potential.

Magnetoreception in the wood mouse (Apodemus sylvaticus): influence of weak frequency-modulated radio frequency fields

The mammalian magnetic sense is predominantly studied in species with reduced vision such as mole-rats and bats. Far less is known about surface-dwelling (epigeic) rodents with well-developed eyes. Here, we tested the wood mouse Apodemus sylvaticus for magnetoreception using a simple behavioural assay in which mice are allowed to build nests overnight in a visually symmetrical, circular arena. The tests were performed in the ambient magnetic field or in a field rotated by 90°. When plotted with respect to magnetic north, the nests were bimodally clustered in the northern and southern sectors, clearly indicating that the animals used magnetic cues. Additionally, mice were tested in the ambient magnetic field with a superimposed radio frequency magnetic field of the order of 100 nT. Wood mice exposed to a 0.9 to 5 MHz frequency sweep changed their preference from north-south to east-west. In contrast to birds, however, a constant frequency field tuned to the Larmor frequency (1.33 MHz) had no effect on mouse orientation. In sum, we demonstrated magnetoreception in wood mice and provide first evidence for a radical-pair mechanism in a mammal.

Directional compass preference for landing in water birds

IntroductionLanding flight in birds is demanding on visual control of velocity, distance to target, and slope of descent. Birds flying in flocks must also keep a common course of landing in order to avoid collisions. Whereas the wind direction may provide a cue for landing, the nature of the landing direction indicator under windless conditions has been unknown. We recorded and analysed landing directions of 3,338 flocks in 14 species of water birds in eight countries.ResultsWe show that the preferred landing direction, independently of the direction from which the birds have arrived, is along the north-south axis. We analysed the effect of the time of the year, time of the day (and thus sun position), weather (sunny versus overcast), light breeze, locality, latitude, and magnetic declination in 2,431 flocks of mallards (Anas platyrhynchos) and found no systematic effect of these factors upon the preferred direction of landing. We found that magnetic North was a better predictor for landing direction than geographic North.ConclusionsIn absence of any other common denominator determining the landing direction, the alignment with the magnetic field lines seems to be the most plausible if not the only explanation for the directional landing preference under windless and overcast conditions and we suggest that the magnetic field thus provides a landing direction indicator.

Compass-controlled escape behavior in roe deer

We tested the hypothesis that magnetic alignment, a tendency to align the body axis with a certain angle to the field lines of the geomagnetic field, provides direction indicator (the so-called nonsense orientation) also in mammals. We measured alignment of free-ranging (grazing or standing) roe deer and the compass direction of their escape trajectories as well as the direction from the threat and to the next shelter. Roe deer were significantly nonrandomly aligned along the north-south axis when grazing. In 188 provocations performed in open flat habitats, deer also tended to escape along this axis and avoided to escape westwards or eastwards. Thus, in many provocations (those from east or west), animals fled at wide angles, either northwards or southwards and not straight away from the threat, a strategy that would maximize the distance between the animal and the danger. Since all the factors which might influence direction of escape (sun position, wind direction, direction to the shelter, straight direction from danger) were randomly distributed in time and space, they constitute just statistical noise which does not add. The only common denominator of all data sets was the magnetic field. We conclude that the north-south alignment expresses the readiness to escape along this axis and might help to synchronize the movement and cohesion of the group and also supports mental mapping of space.Significance statementThis is the first study of escape behavior in animals which considers also the role of absolute compass direction. Our findings confirm existence of magnetic alignment and thus magnetosensitivity in the roe deer and provide first evidence for its role as the so-called direction indicator in control of escape behavior in roe deer in particular and in mammals in general. Our results make the speculations more plausible that the magnetic alignment helps to organize and read the mental (cognitive) map of space. (In analogy, humans are more efficient in reading and commenting the map, if it is held in an accustomed direction: with north pointing upwards and if the person aligns with the map and with the visible landmarks.)

Sexual dimorphism of cranial measurements in the red fox Vulpes vulpes (Canidae, Carnivora) from the Czech Republic

Abstract. For the evaluation of sexual dimorphism 739 red fox skulls (including 433 males and 306 females) from the Czech Republic were examined. The individuals younger than six months were excluded from the study of sexual dimorphism and the rest was divided into three age classes (individuals at the age of 6.5–12 months, 12.5–24 months and 24.5 months and older). Skull size differences between males and females were significant in all age classes. Males exceeded females in all dimensions with the exception of postorbital breadth, which was wider in females. Other skull shape differences between males and females were not confirmed. Age class including individuals 12.5–24 months old was the only, in which significant skull shape differences were found. We suppose that competition between males could play the major role in sexual dimorphism formation.

Cranial ontogenetic variability, sex ratio and age structure of the Red fox

Describing the sex ratio, age structure of the population and ontogenetic variability of Red fox, Vulpes vulpes (Canidae, Carnivora) skull parameters, this study is based on 416 male and 289 female skulls collected in the Czech Republic. The skulls analysed came from feral individuals, that were shot by hunters. The male to female ratio was 1:0.69 regarding the whole population. Individuals younger than one year prevailed in the population (54% males, 48% females were in their first year of life). Four growth patterns of skull dimensions were described. The first group included mainly skull length dimensions (e.g. condylobasal length). They grew rapidly until the sixth month of life, becoming stabilised afterwards. The second group comprised parameters that were stable throughout the life (e.g. cheek tooth rows). Measurements representing the third growth pattern showed continual growth (mainly width dimensions, e.g. zygomatic breadth). Conversely, smaller dimensions of postorbital breadth were observed after the sixth month of life. Postorbital breadth represented the fourth growth pattern. It was concluded, that male and female Red foxes had similar ontogenetic skull development, even though there were some differences, e.g. in jugular breadth, which increased after the age of six months in males unlike in females.

Effect of habitat and game management practices on ring-necked pheasant harvest in the Czech Republic

The ring-necked pheasant (Phasianus colchicus L.) is one of the most popular small game species both numerically and economically. Pheasant populations are commonly managed in the Czech Republic in order to maximize their harvest. Game managers need to be aware of the possible effects of different management tools on wild pheasant populations. We used data from 38 hunting grounds collected over an 8-year period (2004–2011) and generalized linear mixed effects models (GLMMs) to assess whether pheasant harvest was related to the habitat characteristics and game management practices (release of hand-reared individuals and predator control) in the Czech Republic. The proportion of grasslands, idle lands (spontaneously set-aside lands), and organically farmed lands (i.e., with limited use of industrially made fertilizers and pesticides) and the density of watercourses were positively related to the pheasant harvest. The proportion of forests and road density showed a negative relationship with the pheasant harvest. An important effect of year on the pheasant harvest was also found. In terms of game management practices, predator control intensity (i.e., foxes, martens, corvids) was positively related to the pheasant harvest. The release of hand-reared individuals was not included in the final GLMMs. Our study suggests that the best long-term strategy to reinforce the wild population of ring-necked pheasants would be to concentrate on habitat improvement through the implementation of set-aside management, maintaining the right percentage of shrubby and grass vegetation, to continue with targeted predator control, and to reduce the costly practice of releasing of hand-reared individuals.

Use of bio-loggers to characterize red fox behavior with implications for studies of magnetic alignment responses in free-roaming animals

Background Spontaneous magnetic alignment (SMA), in which animals position their body axis in fixed alignments relative to magnetic field lines, has been shown in several classes of vertebrates and invertebrates. Although these responses appear to be widespread, the functional significance and sensory mechanism(s) underlying SMA remain unclear. An intriguing example comes from observations of wild red foxes (Vulpes vulpes) that show a ~fourfold increase in hunting success when predatory ‘mousing’ attacks are directed toward magnetic north-northeast. This form of SMA is proposed to receive input from a photoreceptor-based magnetoreception mechanism perceived as a ‘visual pattern’ and used as a targeting system to increase the accuracy of mousing attempts targeting hidden prey. However, similar to previous observational studies of magnetic orientation in vertebrates, direct evidence for the use of magnetic cues, and field-based experiments designed to characterize the biophysical mechanisms of SMA are lacking. Here, we develop a new approach for studies of SMA using triaxial accelerometer and magnetometer bio-loggers attached to semidomesticated red foxes.ResultsAccelerometer data were recorded from 415 ground-truth events of three behaviors exhibited by an adult red fox. A 5-nearest neighbor classifier was developed for behavioral analysis and performed with an accuracy of 95.7% across all three behaviors. To evaluate the generalizability of the classifier, data from a second fox were tested yielding an accuracy of 66.7%, suggesting the classifier can extract behaviors across multiple foxes. A similar classification approach was used to identify the fox’s magnetic alignment using two 8-way classifiers with differing underlying assumptions to distinguish magnetic headings in eight equally spaced 45° sectors. The magnetic heading classifiers performed with 90.0 and 74.2% accuracy, suggesting a realistic performance range for a classifier based on an independent set of training events equal in size to our sample.ConclusionsWe report the development of ‘magnetic ethograms’ in which the behavior and magnetic alignment of foxes can be accurately extracted from raw sensor data. These techniques provide the basis for future studies of SMA where direct observation is not necessary and may allow for more sophisticated experimental designs aimed to characterize the sensory mechanisms mediating SMA behavior.

First findings of brown hare (Lepus europaeus) reintroduction in relation to seasonal impact

In Europe, brown hare (Lepus europaeus) populations have been declining steadily since the 1970s. Gamekeepers can help to support brown hare wild populations by releasing cage-reared hares into the wild. Survival rates of cage-reared hares has been investigated in previous studies, however, survival times in relation to seasonality, which likely plays a crucial role for the efficacy of this management strategy, has not been evaluated. Here we examine the survival duration and daytime home ranges of 22 hares released and radio-tracked during different periods of the year in East Bohemia, Czech Republic. The majority of hares (82%) died within the first six months after release, and 41% individuals died within the first 10 days. Significant differences were found in the duration of survival with respect to the release date. Hares released in the summer months (July and August) survived the longest (on average 103.2 days, SD ± 23.8) and hares released throughout all other months of the year survived for significantly shorter periods of time (on average 20.4 days, SD ± 11.5). The most likely cause of death was red fox predation (38.9%) followed by disease (coccidiosis and other health problems) (27.8%). Three hares (16.6%) were killed by automobile traffic. After six months of radiotracking, we found the average survival time of all hares released was 58 (SD ± 70.9) days. Hares in this study preferred to remain in the vicinity of the release area and the average distance from release point to the center of the home range was 471 m.